Re: [Freetel-codec2] Gnuradio Modem/demod design for experiments with HF-equipment

[Gerhard B. <ger...@ut...>]

Hello Hartje!

 

Many thanks for that.

 

I really have problems to install gnuradio 3.5. So at the very moment I have
Fedora Rawhide running an I am installing gnuradio 3.5 and GRC 0.70.

I hope the preliminary version of Fedora is OK.

So, you say, with your module we also can use grnuradio 3.2.2? Without the
codec2-blocks?

That is great as we can use stable linux versions.

Will try it this evening!

 

Best regards

Gerhard OE3GBB

 

 

 

Von: Michael Hartje [mailto:ha...@et...] 
Gesendet: Dienstag, 20. Dezember 2011 23:52
An: fre...@li...
Betreff: [Freetel-codec2] Gnuradio Modem/demod design for experiments with
HF-equipment

 

dear fellows,

the attached archive is the current version of my design of a modem with
gnuradio. This modem has the objective to enable a very narrow-band
modulation of the codec2 data stream.

Included in the archive are the
* Input files for gnuradio Companion v3.5.0
* Figure 1 shows the modem
* Figure 2 shows the demodulator
* executable python code obtained from the GRC file


With this modem, we can achieve with QPSK about 1.4 bits / Hz and QAM16
(OFDM) with approximately 3.2 bits / Hz.

Now for the very small stream with codec2 (1400 bit / s) so we can transfer
into a normal audio channel on the radio two parallel voice channels!

The modem uses a structure with the following 7 steps described below:

1. Microphone input of the soundcard
2. Gnuradio with Amplifier and Converter to raw
3. File Encoder pipeline for codec2
4. File Encoder pipeline of codec2
5. Codestream process with QPSK or OFDM
6. mixer up to e.g. 1 kHz
7. Output to the TX (Sondkarte)

Since the sound cards have two channels, one can even  send TX and RX audio
streams into the two channels - not shown.

The arrangement in the demodulator is accordingly reversed.

I myself have been involved since 2008 with gnuradio. For the first time on
the IPRT (International Packet Radio Conference) in March 2009, Darmstadt,
Germany I have reported it. (www.iprt.de) In another contribution during the
conference I have shown a similar modem - but without codec2 - and discussed
it in a workshop.

Instructions for use of gnuradio-companion:
If you have an older version of gnuradio allready installed, use it! If so,
you can use it since the only use of hardware is the soundcard. (Version
3.2.2 GR and GRC is sufficient). 
The shaded portions of the image is currently at time of the picture)
disabled. The resulting built executable Python file does not contain these
parts.

You can select the necessary parts and change the graphical elements and
their parameters.

Of course, we can expand the GR design and also a channel with noise,
interference and distortion can be easily implemented. Therefore we remove
the radio channel and connect the modem and demod via our channel model. In
GR, there are many examples, and of course the necessary modules are in the
GR library.

I would be happy if this idea can stimulate your own experiments. I have
prepared an article for the upcoming IPRT. Does anyone want to work together
with me in it?

thanks for this great development of the Codec2 that has inspired my own
experiments

Michael Hartje
DK5HH